Method and apparatus for receiving control information through blind decoding of an enhanced physical downlink control channel (EPDCCH)

ABSTRACT

One embodiment of the present invention provides a method for enabling a terminal to receive control information in a wireless communication system, comprising the steps of: determining resource units for Enhanced Physical Downlink Control Channel (EPDCCH) of a plurality of resource units, with respect to each of one or more resource sets; and blind-decoding the resource units for the EPDCCH with respect to each of the one or more resource sets, wherein each of the one or more resource sets is set for one of localized EPDCCH transmission or distributed EPCCH transmission.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/209,451, filed on Jul. 13, 2016, now U.S. Pat. No. 9,615,365, whichis a continuation of U.S. patent application Ser. No. 14/384,142, filedSep. 9, 2014, now U.S. Pat. No. 9,445,413, which is the National Stagefiling under 35 U.S.C. 371 of International Application No.PCT/KR2013/002407, filed on Mar. 22, 2013, which claims the benefit ofearlier filing date and right of priority to Korean Application No10-2013-0030996, filed on Mar. 22, 2013 and also claims the benefit ofU.S. Provisional Application Nos. 61/614,495, filed on Mar. 22, 2012,61/617,032, filed on Mar. 28, 2012, 61/617,673, filed on Mar. 30, 2012,61/621,001, filed on Apr. 6, 2012 and 61/682,743, filed on Aug. 13,2012, the contents of which are all hereby incorporated by referenceherein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method and apparatus for receiving controlinformation through an enhanced physical downlink control channel(EPDCCH).

BACKGROUND ART

Wireless communication systems are widely deployed to provide variouskinds of communication content such as voice and data. Generally, thesecommunication systems are multiple access systems capable of supportingcommunication with multiple users by sharing available system resources(e.g., bandwidth and transmit power). Examples of multiple accesssystems include a code division multiple access (CDMA) system, afrequency division multiple access (FDMA) system, a time divisionmultiple access (TDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, a single carrier frequency-division multipleaccess (SC-FDMA) system, and a multi-carrier frequency division multipleaccess (MC-FDMA) system.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method for receiving control information through blind decoding of theEPDCCH.

It is to be understood that technical objects to be achieved by thepresent invention are not limited to the aforementioned technical objectand other technical objects which are not mentioned herein will beapparent from the following description to one of ordinary skill in theart to which the present invention pertains.

Technical Solution

According to a first aspect of the present invention, provided herein isa method for receiving control information by a user equipment (UE) in awireless communication system, including performing blind decoding on aplurality of resource units corresponding to each of at least oneresource set, wherein the resource units are resource units for anenhanced physical downlink control Channel (EPDCCH) among resource unitsrelated to a downlink bandwidth; and each of the at least one resourceset is configured for one of localized EPDCCH transmission anddistributed EPCCH transmission.

According to a second aspect of the present invention, provided hereinis a user equipment in a wireless communication system, including areceive module; and a processor, wherein the processor performs blinddecoding on a plurality of resource units corresponding to each of atleast one resource set, wherein the resource units are resource unitsfor an enhanced physical downlink control channel (EPDCCH) amongresource units related to a downlink bandwidth, and each of the at leastone resource set is configured for one of localized EPDCCH transmissionand distributed EPCCH transmission.

The first and second aspects of the present invention may include thefollowing details.

Each of the resource units may be a physical resource block (PRB) pair,and the resource set is a PRB set.

information indicating that each of the at least one resource set isconfigured for either the localized EPDCCH transmission or thedistributed EPCCH transmission may be signaled to the UE through higherlayer signaling.

Determination of the resource units for the EPDCCH may be based oninformation about a resource set delivered through higher layersignaling.

The at least one resource set may include a first resource setconfigured for the localized EPDCCH transmission and a second resourceset configured for the distributed EPDCCH transmission, and when anoverlapping resource unit included in both the first and second resourcesets is present among the resource units for the EPDCCH, the UE mayconsider only at least one antenna port other than at least one antennaport related to the distributed EPDCCH transmission as valid on theoverlapping resource unit, among at least one antenna port related tothe localized EPDCCH transmission.

The at least one resource set may include a first resource setconfigured for the localized EPDCCH transmission and a second resourceset configured for the distributed EPDCCH transmission; and when anoverlapping resource unit included in both the first and second resourcesets is present among the resource units for the EPDCCH, the UE may usea pre-configured antenna port to perform blind decoding for a localizedEPDCCH on the overlapping resource unit.

The pre-configured antenna port may be delivered through higher layersignaling.

The at least one antenna port related to the localized EPDCCHtransmission may include antenna ports 107, 108, 109, and 110, and theat least one antenna port related to the distributed EPDCCH transmissionmay include antenna ports 107 and 109.

The PRB pair may include four enhanced control channel elements (ECCEs).

Each of the ECCEs may include four enhanced resource element groups(EREGs).

The localized EPDCCH transmission may be based on at least oneconsecutive ECCE according to aggregation level.

The distributed EPDCCH transmission may be based on an ECCE includingEREGs belonging to PRB pairs.

Advantageous Effects

According to embodiments of the present invention, blind decoding may beefficiently performed according to the transmission type of the EPDCCH.

It will be appreciated by those skilled in the art that the effects thatcan be achieved with the present invention are not limited to what hasbeen described above and other advantages of the present invention willbe clearly understood from the following detailed description taken inconjunction with the accompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 illustrates a radio frame structure.

FIG. 2 is a diagram illustrating a resource grid for one downlink (DL)slot.

FIG. 3 is a diagram illustrating a DL subframe structure.

FIG. 4 is a diagram illustrating an uplink (UL) subframe structure.

FIG. 5 illustrates a search space.

FIG. 6 illustrates a reference signal.

FIGS. 7 and 8 are diagrams illustrating blind decoding/search spaceconfiguration for EPDCCH according to one embodiment of the presentinvention.

FIG. 9 is a diagram illustrating a method for performing antenna portmapping and decoding according to one embodiment of the presentinvention.

FIG. 10 is a diagram illustrating a method for configuring an EPDCCHcandidate and a method for performing decoding according to oneembodiment of the present invention.

FIG. 11 illustrates an EPDCCH resource set and antenna port mappingaccording to one embodiment of the present invention.

FIGS. 12 to 14 illustrate port allocation in the case in which localizedEPDCCH transmission and distributed EPDCCH transmission are mixed in onePRB pair according to one embodiment of the present invention.

FIG. 15 is a diagram illustrating determination of the number of antennaports for each PRB pair.

FIGS. 16 and 17 are diagrams illustrating allocation of a search spaceaccording to one embodiment of the present invention.

FIG. 18 is a diagram illustrating a relationship between an EPDCCH and ademodulation RS port according to one embodiment of the presentinvention.

FIG. 19 is a diagram illustrating configuration of transceivers.

BEST MODE

The embodiments described below are constructed by combining elementsand features of the present invention in a predetermined form. Theelements or features may be considered selective unless explicitlymentioned otherwise. Each of the elements or features can be implementedwithout being combined with other elements. In addition, some elementsand/or features may be combined to configure an embodiment of thepresent invention. The sequence of the operations discussed in theembodiments of the present invention may be changed. Some elements orfeatures of one embodiment may also be included in another embodiment,or may be replaced by corresponding elements or features of anotherembodiment.

Embodiments of the present invention will be described focusing on adata communication relationship between a base station and a terminal.The base station serves as a terminal node of a network over which thebase station directly communicates with the terminal. Specificoperations illustrated as being conducted by the base station in thisspecification may be conducted by an upper node of the base station, asnecessary.

In other words, it will be obvious that various operations allowing forcommunication with the terminal in a network composed of several networknodes including the base station can be conducted by the base station ornetwork nodes other than the base station. The term “base station (BS)”may be replaced with terms such as “fixed station,” “Node-B,” “eNode-B(eNB),” and “access point”. The term “relay” may be replaced with suchterms as “relay node (RN)” and “relay station (RS)”. The term “terminal”may also be replaced with such terms as “user equipment (UE),” “mobilestation (MS),” “mobile subscriber station (MSS)” and “subscriber station(SS)”.

It should be noted that specific terms disclosed in the presentinvention are proposed for convenience of description and betterunderstanding of the present invention, and these specific terms may bechanged to other formats within the technical scope or spirit of thepresent invention.

In some cases, known structures and devices may be omitted or blockdiagrams illustrating only key functions of the structures and devicesmay be provided, so as not to obscure the concept of the presentinvention. The same reference numbers will be used throughout thisspecification to refer to the same or like parts.

Exemplary embodiments of the present invention are supported by standarddocuments for at least one of wireless access systems including aninstitute of electrical and electronics engineers (IEEE) 802 system, a3rd generation partnership project (3GPP) system, a 3GPP long termevolution (LTE) system, an LTE-advanced (LTE-A) system, and a 3GPP2system. In particular, steps or parts, which are not described in theembodiments of the present invention to prevent obscuring the technicalspirit of the present invention, may be supported by the abovedocuments. All terms used herein may be supported by the above-mentioneddocuments.

The embodiments of the present invention described below can be appliedto a variety of wireless access technologies such as code divisionmultiple access (CDMA), frequency division multiple access (FDMA), timedivision multiple access (TDMA), orthogonal frequency division multipleaccess (OFDMA), and single carrier frequency division multiple access(SC-FDMA). CDMA may be embodied through wireless technologies such asuniversal terrestrial radio access (UTRA) or CDMA2000. TDMA may beembodied through wireless technologies such as global system for mobilecommunication (GSM)/general packet radio service (GPRS)/enhanced datarates for GSM evolution (EDGE). OFDMA may be embodied through wirelesstechnologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802-20, and evolved UTRA (E-UTRA). UTRA is a part of universal mobiletelecommunications system (UMTS). 3rd generation partnership project(3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS),which uses E-UTRA. 3GPP LTE employs OFDMA for downlink and employsSC-FDMA for uplink. LTE-Advanced (LTE-A) is an evolved version of 3GPPLTE. WiMAX can be explained by IEEE 802.16e (wirelessMAN-OFDMA referencesystem) and IEEE 802.16m advanced (wirelessMAN-OFDMA advanced system).For clarity, the following description focuses on 3GPP LTE and 3GPPLTE-A systems. However, the spirit of the present invention is notlimited thereto.

Hereinafter, a radio frame structure will be described with reference toFIG. 1.

In a cellular OFDM wireless packet communication system, an uplink(UL)/downlink (DL) data packet is transmitted on a subframe-by-subframebasis, and one subframe is defined as a predetermined time intervalincluding a plurality of OFDM symbols. 3GPP LTE supports a type-1 radioframe structure applicable to frequency division duplex (FDD) and atype-2 radio frame structure applicable to time division duplex (TDD).

FIG. 1(a) illustrates the type-1 radio frame structure. A downlink radioframe is divided into ten subframes. Each subframe includes two slots inthe time domain. The time taken to transmit one subframe is defined as atransmission time interval (TTI). For example, a subframe may have aduration of 1 ms and one slot may have a duration of 0.5 ms. A slot mayinclude a plurality of OFDM symbols in the time domain and a pluralityof resource blocks (RBs) in the frequency domain. Since 3GPP LTE employsOFDMA for downlink, an OFDM symbol represents one symbol period. An OFDMsymbol may be referred to as an SC-FDMA symbol or a symbol period. Aresource block (RB), which is a resource allocation unit, may include aplurality of consecutive subcarriers in a slot.

The number of OFDM symbols included in one slot depends on theconfiguration of a cyclic prefix (CP). CPs are divided into an extendedCP and a normal CP. For a normal CP configuring each OFDM symbol, a slotmay include 7 OFDM symbols. For an extended CP configuring each OFDMsymbol, the duration of each OFDM symbol is extended and thus the numberof OFDM symbols included in a slot is smaller than in the case of thenormal CP. For the extended CP, a slot may include, for example, 6 OFDMsymbols. When a channel status is unstable as in the case of high speedmovement of a UE, the extended CP may be used to reduce inter-symbolinterference.

When the normal CP is used, each slot includes 7 OFDM symbols, and thuseach subframe includes 14 OFDM symbols. In this case, the first two orthree OFDM symbols of each subframe may be allocated to a physicaldownlink control channel (PDCCH) and the other three OFDM symbols may beallocated to a physical downlink shared channel (PDSCH).

FIG. 1(b) illustrates the type-2 radio frame structure. The type-2 radioframe includes two half frames, each of which has 5 subframes, adownlink pilot time slot (DwPTS), a guard period (GP), and an uplinkpilot time slot (UpPTS). Each subframe includes two slots. The DwPTS isused for initial cell search, synchronization, or channel estimation ina UE, whereas the UpPTS is used for channel estimation in an eNB and ULtransmission synchronization in a UE. The GP is provided to eliminateinterference taking place in UL due to multipath delay of a DL signalbetween DL and UL. Regardless of the type of a radio frame, a subframeof the radio frame includes two slots.

The illustrated radio frame structures are merely examples, and variousmodifications may be made to the number of subframes included in a radioframe, the number of slots included in a subframe, or the number ofsymbols included in a slot.

FIG. 2 is a diagram illustrating a resource grid for one DL slot. A DLslot includes 7 OFDM symbols in the time domain and an RB includes 12subcarriers in the frequency domain. However, embodiments of the presentinvention are not limited thereto. For a normal CP, a slot may include 7OFDM symbols. For an extended CP, a slot may include 6 OFDM symbols.Each element in the resource grid is referred to as a resource element(RE). An RB includes 12×7 REs. The number NDL of RBs included in adownlink slot depends on a DL transmission bandwidth. A UL slot may havethe same structure as a DL slot.

FIG. 3 illustrates a DL subframe structure. Up to the first three OFDMsymbols of the first slot in a DL subframe are used as a control regionto which control channels are allocated and the other OFDM symbols ofthe DL subframe are used as a data region to which a PDSCH is allocated.DL control channels used in 3GPP LTE include, for example, a physicalcontrol format indicator channel (PCFICH), a physical downlink controlchannel (PDCCH), and a physical hybrid automatic repeat request (HARQ)indicator channel (PHICH). The PCFICH is transmitted in the first OFDMsymbol of a subframe, carrying information about the number of OFDMsymbols used for transmission of control channels in the subframe. ThePHICH carries a HARQ ACK/NACK signal in response to uplink transmission.Control information carried on the PDCCH is called downlink controlinformation (DCI). The DCI includes UL or DL scheduling information orUL transmit power control commands for UE groups. The PDCCH deliversinformation about resource allocation and a transport format for a DLshared channel (DL-SCH), resource allocation information about a ULshared channel (UL-SCH), paging information of a paging channel (PCH),system information on the DL-SCH, information about resource allocationfor a higher-layer control message such as a random access responsetransmitted on the PDSCH, a set of transmit power control commands forindividual UEs of a UE group, transmit power control information, andvoice over internet protocol (VoIP) activation information. A pluralityof PDCCHs may be transmitted in the control region. A UE may monitor aplurality of PDCCHs. A PDCCH is formed by aggregating one or moreconsecutive control channel elements (CCEs). A CCE is a logicalallocation unit used to provide a PDCCH at a coding rate based on thestate of a radio channel. A CCE corresponds to a plurality of RE groups.The format of a PDCCH and the number of available bits for the PDCCH aredetermined depending on the correlation between the number of CCEs and acoding rate provided by the CCEs. An eNB determines the PDCCH formataccording to DCI transmitted to a UE and adds a cyclic redundancy check(CRC) to the control information. The CRC is masked by an identifier(ID) known as a radio network temporary identifier (RNTI) according tothe owner or usage of the PDCCH. If the PDCCH is directed to a specificUE, its CRC may be masked by a cell-RNTI (C-RNTI) of the UE. If thePDCCH is for a paging message, the CRC of the PDCCH may be masked by apaging radio network temporary identifier (P-RNTI). If the PDCCHdelivers system information, particularly, a system information block(SIB), the CRC thereof may be masked by a system information ID and asystem information RNTI (SI-RNTI). To indicate that the PDCCH delivers arandom access response in response to a random access preambletransmitted by a UE, the CRC thereof may be masked by a randomaccess-RNTI (RA-RNTI).

FIG. 4 illustrates a UL subframe structure. A UL subframe may be dividedinto a control region and a data region in the frequency domain. Aphysical uplink control channel (PUCCH) carrying uplink controlinformation is allocated to the control region and a physical uplinkshared channel (PUSCH) carrying user data is allocated to the dataregion. To maintain single carrier property, a UE does notsimultaneously transmit a PUSCH and a PUCCH. A PUCCH for a UE isallocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. This is often called frequencyhopping of the RB pair allocated to the PUCCH over a slot boundary.

DCI Format

DCI formats 0, 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3, 3A and 4 are definedin LTE-A (Release 10). DCI formats 0, 1A, 3 and 3A are defined to havethe same message size to reduce the number of times of blind decoding,which will be described later. The DCI formats may be divided into i)DCI formats 0 and 4 used for uplink grant, ii) DCI formats 1, 1A, 1B,1C, 1D, 2, 2A, 2B and 2C used for downlink scheduling allocation, andiii) DCI formats 3 and 3A for power control commands according topurposes of use of control information to be transmitted.

DCI format 0 used for uplink grant may include a carrier indicatornecessary for carrier aggregation, which will be described later, anoffset (flag for format 0/format 1A differentiation) used todifferentiate DCI formats 0 and 1A from each other, a frequency hoppingflag that indicates whether frequency hopping is used for uplink PUSCHtransmission, information about resource block assignment, used for a UEto transmit a PUSCH, a modulation and coding scheme, a new dataindicator used to empty a buffer for initial transmission in relation toa HARQ process, a transmit power control (TPC) command for a scheduledPUSCH, information about a cyclic shift for a demodulation referencesignal (DMRS) and OCC index, and a UL index and channel qualityindicator request (CSI request) necessary for a TDD operation, etc. DCIformat 0 does not include a redundancy version, unlike DCI formatsrelating to downlink scheduling allocation since DCI format 0 usessynchronous HARQ. The carrier indicator is not included in DCI formatswhen cross-carrier scheduling is not used.

DCI format 4, which is newly added to DCI formats in LTE-A Release 10,supports application of spatial multiplexing to uplink transmission inLTE-A. DCI format 4 has a larger message size DCI format 0 because itfurther includes information for spatial multiplexing. DCI format 4includes additional control information in addition to controlinformation included in DCI format 0. That is, DCI format 4 includesinformation on a modulation and coding scheme for the secondtransmission block, precoding information for multi-antennatransmission, and sounding reference signal (SRS) request information.DCI format 4 does not include an offset for differentiation betweenformats 0 and 1A because it has a larger size than DCI format 0.

DCI formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B and 2C for downlink schedulingallocation may be broadly divided into DCI formats 1, 1A, 1B, 1C and 1D,which do not support spatial multiplexing, and DCI formats 2, 2A, 2B and2C, which support spatial multiplexing.

DCI format 1C supports only frequency contiguous allocation as compactfrequency allocation and does not include the carrier indicator andredundancy version, compared to the other formats.

DCI format 1A is for downlink scheduling and random access. DCI format1A may include a carrier indicator, an indicator that indicates whetherdownlink distributed transmission is used, PDSCH resource allocationinformation, a modulation and coding scheme, a redundancy version, aHARQ processor number for indicating a processor used for softcombining, a new data indicator used to empty a buffer for initialtransmission in relation to a HARQ process, a TPC command for a PUCCH,an uplink index necessary for a TDD operation, etc.

DCI format 1 includes control information similar to that of DCI format1A. DCI format 1 supports non-contiguous resource allocation, while DCIformat 1A is related to contiguous resource allocation. Accordingly, DCIformat 1 further includes a resource allocation header, and thusslightly increases control signaling overhead as a trade-off for anincrease in flexibility of resource allocation.

Both DCI formats 1B and 1D further include precoding information,compared to DCI format 1. DCI format 1B includes PMI acknowledgement andDCI format 1D includes downlink power offset information. Most controlinformation included in DCI formats 1B and 1D corresponds to that of DCIformat 1A.

DCI formats 2, 2A, 2B and 2C basically include most control informationincluded in DCI format 1A and further include information for spatialmultiplexing. The information for spatial multiplexing includes amodulation and coding scheme for the second transmission block, a newdata indicator, and a redundancy version.

DCI format 2 supports closed loop spatial multiplexing, and DCI format2A supports open loop spatial multiplexing. Both DCI formats 2 and 2Ainclude precoding information. DCI format 2B supports dual layer spatialmultiplexing combined with beamforming and further includes cyclic shiftinformation for a DMRS. DCI format 2C, which may be regarded as anextended version of DCI format 2B, supports spatial multiplexing for upto 8 layers.

DCI formats 3 and 3A may be used to complement the TPC informationincluded in the aforementioned DCI formats for uplink grant and downlinkscheduling allocation, namely, to support semi-persistent scheduling. A1-bit command is used per UE in the case of DCI format 3, while a 2-bitcommand is used per UE in the case of DCI format 3A.

One of the DCI formats described above is transmitted through a PDCCH,and a plurality of PDCCHs may be transmitted in a control region. A UEmay monitor the plurality of PDCCHs.

PDCCH Processing

Control channel elements (CCEs), contiguous logical allocation units,are used to map a PDCCH to REs for efficient processing. A CCE includesa plurality of resource element groups (e.g., 9 REGs). Each REG includesfour neighboring REs other than an RS.

The number of CCEs necessary for a specific PDCCH depends on a DCIpayload corresponding to a control information size, a cell bandwidth, achannel coding rate, etc. Specifically, the number of CCEs for aspecific PDCCH may be defined according to PDCCH formats as shown inTable 1.

TABLE 1 Number of PDCCH format Number of CCEs Number of REGs PDCCH bits0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

As described above, one of the four formats may be used for a PDCCH andis not known to the UE. Accordingly, the UE performs decoding withoutknowing the PDCCH format. This is called blind decoding. Since operationoverhead is generated if a UE decodes all the CCEs usable for downlinkfor each PDCCH, a search space is defined in consideration ofrestriction on a scheduler and the number of decoding attempts.

That is, the search space is a set of candidate PDCCHs composed of CCEson which a UE needs to attempt to perform decoding at an aggregationlevel. Each aggregation level and the corresponding number of candidatePDCCHs may be defined as shown in

TABLE 2 Search space Number of PDCCH Aggregation level Size (CCE unit)candidates UE-specific 1 6 6 2 12 6 4 8 2 8 16 2 Common 4 16 4 8 16 2

As shown Table 2, the UE has a plurality of search spaces at eachaggregation level because 4 aggregation levels are present. The searchspaces may be divided into a UE-specific search space and a commonsearch space, as shown in Table 2. The UE-specific search space is forspecific UEs. Each UE may check an RNTI and CRC which mask a PDCCH bymonitoring a UE-specific search space thereof (attempting to decode aPDCCH candidate set according to an available DCI format) and acquirecontrol information when the RNTI and CRC are valid.

The common search space (CSS) is used for a case in which a plurality ofUEs or all UEs need to receive PDCCHs, for system information dynamicscheduling or paging messages, for example. The CSS may be used for aspecific UE for resource management. Furthermore, the CSS may overlapthe UE-specific search space. The control information for the UEs may bemasked by one of RA-RNTI, SI-RNTI and P-RNTI.

Specifically, the search space may be determined by Equation 1 givenbelow.L{(Y _(k) +m′)mod └N _(CCE,k) /L┘}+i  Equation 1

Here, L denotes an aggregation level, Y_(k) is a variable determined byan RNTI and subframe number k, and m′ is the number of PDCCH candidates.If carrier aggregation is applied, m′=m+M^((L))·n_(Cl) and otherwise,m′=m. Herein, M^((L)) is the number of PDCCH candidates. N_(CCE,k) isthe total number of CCEs in the control region of a k-th subframe, and iis a factor indicating an individual CCE in each PDCCH candidate and isset as i=0, 1, . . . , L−1. For the CSS, Y_(k) is always determined tobe 0.

FIG. 5 shows USSs (shaded portions) at respective aggregation levelswhich may be defined according to Equation 1. Carrier aggregation is notused, and N_(CCE,k) is set to 32 for simplicity of illustration.

FIGS. 5(a), 5(b), 5(c) and 5(d) illustrate the cases of aggregationlevels 1, 2, 4 and 8, respectively. The numbers represent CCE numbers.In FIG. 5, the start CCE of a search space at each aggregation level isdetermined based on an RNTI and subframe number k. This CCE may bedifferently determined among the aggregations levels in the samesubframe for a UE due to the modulo function and L. The CCE is alwaysdetermined to correspond to a multiple of the aggregation level due toL. In the description given below, Y_(k) is assumed to be CCE 18. The UEattempts to sequentially perform decoding from the start CCE in units ofCCEs determined for a corresponding aggregation level. In FIG. 5(b), forexample, The UE attempts to perform decoding from CCE 4, the start CCE,for every two CCEs according to the aggregation levels.

In this manner, the UE attempts to perform decoding for a search space.The number of decoding attempts is determined by a DCI format and atransmission mode determined through radio resource control (RRC)signaling. If carrier aggregation is not applied, the UE needs toattempt to perform decoding up to 12 times in a CSS, in consideration oftwo DCI sizes (DCI formats 0/1A/3/3A and DCI format 1C) for each of sixPDCCH candidates. In a USS, the UE needs to attempt to perform decodingup to 32 times, in consideration of two DCI sizes for each of 16 PDCCHcandidates (6+6+2+2=16). Accordingly, when carrier aggregation is notapplied, the UE needs to attempt to perform decoding up to 44 times.

On the other hand, if carrier aggregation is applied, the maximum numberof decodings increases because as many decodings for a USS and DCIformat 4 as the number of DL resources (DL component carriers) areadded.

Reference Signal (RS)

In transmitting packets in a wireless communication system, the packetsare transmitted over a radio channel, and therefore signal distortionmay occur in the transmission process. For a receiver to receive thecorrect signal in spite of signal distortion, the received distortedsignal should be corrected using channel information. In detecting thechannel information, a signal which is known to both the transmitter andthe receiver is transmitted and the degree of distortion of the signalreceived over the channel is used to detect the channel information.This signal is referred to as a pilot signal or a reference signal.

In the case in which data is transmitted and received using multipleantennas, a channel state between a transmit antenna and a receiveantenna needs to be identified to receive a correct signal. Accordingly,a separate RS is needed for each transmit antenna and, moreparticularly, for each antenna port.

RSs may be divided into a UL RS and a DL RS. In the current LTE system,the UL RSs include:

i) a demodulation-reference signal (DM-RS) for channel estimation forcoherent demodulation of information transmitted over a PUSCH and aPUCCH, and

ii) a sounding reference signal (SRS) for measuring UL channel qualityat frequencies of different networks in the BS.

The DL RSs include:

i) a cell-specific reference signal (CRS) shared by all UEs in a cell;

ii) a UE-specific reference signal for a specific UE;

iii) a demodulation-reference signal (DM-RS) transmitted for coherentdemodulation in the case of transmission of a PDSCH;

iv) a channel state information-reference signal (CSI-RS) for deliveringchannel state information (CSI) in the case of transmission of a DLDMRS;

v) a multimedia broadcast single frequency network (MBSFN) referencesignal transmitted for coherent demodulation of a signal transmitted inan MBSFN mode, and

vi) a positioning reference signal used to estimate geographic positioninformation of a UE.

The RSs may be broadly divided into two reference signals according tothe purposes thereof. There are an RS used to acquire channelinformation and an RS used for data demodulation. Since the former isused when the UE acquires channel information on DL, this RS should betransmitted over a wide band and even a UE which does not receive DLdata in a specific subframe should receive the RS. This RS is alsoapplied to situations such as handover. The latter RS is sent by the BSalong with a resource on DL. The UE may receive the RS to performchannel measurement to implement data modulation. This RS should betransmitted in a region in which data is transmitted.

The CRS is used for acquisition of channel information and for datademodulation, and the UE-specific RS is used only for data demodulation.The CRS is transmitted in every subframe in a wide band and RSs for upto four antenna ports are transmitted according to the number oftransmit antennas of the BS.

For example, if the number of transmit antennas of the BS is 2, CRSs forantenna ports #0 and #1 are transmitted. If the number of transmitantennas of the BS is 4, CRSs for antenna ports #0 to #3 arerespectively transmitted.

FIG. 6 is a diagram illustrating a pattern in which CRSs and DRSsdefined in a legacy 3GPP LTE system (e.g., Release-8) are mapped toresource block (RB) pairs. A downlink RB pair, as a unit to which an RSis mapped, may be represented as a unit of one subframe in the timedomain times 12 subcarriers in the frequency domain. That is, one RBpair has a length of 14 OFDM symbols for a normal CP (FIG. 6(a)) and alength of 12 OFDM symbols for an extended CP (FIG. 6(b)).

FIG. 6 shows locations of RSs on RB pairs in a system in which the BSsupports four transmit antennas. In FIG. 6, resource elements (REs)denoted by “0”, “1”, “2” and “3” represent the locations of the CRSs forantenna port indexes 0, 1, 2 and 3, respectively. In FIG. 6, REs denotedby “D” represent locations of the DMRSs.

In an LTE system after Release 11, an enhanced-PDCCH (EPDCCH) isconsidered as a solution to lack of capacity of a PDCCH due tocoordinated multi-point (CoMP), multi user-multiple input multipleoutput (MU-MIMO), and the like and degradation of PDCCH performance dueto inter-cell interference. In addition, channel estimation may beperformed on an EPDCCH based on DMRSs contrary to the existing CRS-basedPDCCH, in order to obtain a pre-coding gain.

While transmission of the PDCCH described above is performed based onREGs and CCEs configured with REGs, transmission of the EPDCCH may beperformed based on enhanced REGs (EREGs), enhanced CCE (ECCEs), andphysical resource block (PRB) pairs. Each ECCE may include four EREGs,and each PRB pair may include four ECCEs. EPDCCH also employs theconcept of aggregation level as in the case of PDCCH, but theaggregation levels for the EPDCCH are based on ECCEs.

EPDCCH transmission may be divided into localized EPDCCH transmissionand distributed EPDCCH transmission according to configuration of a PRBpair used for EPDCCH transmission. Localized EPDCCH transmissionrepresents a case in which resource sets used for transmission of anEPDCCH neighbor each other in the frequency domain, and precoding may beapplied to obtain a beamforming gain. For example, localized EPDCCHtransmission may be based on consecutive ECCEs the number of whichcorresponds to aggregation level. On the other hand, distributed EPDCCHtransmission represents transmission of an EPDCCH in a separated PRBpair in the frequency domain, and has an advantage with regard tofrequency diversity. For example, distributed EPDCCH transmission may bebased on the ECCE having four EREGs included in each PRB pair separatedin the frequency domain.

Hereinafter, various embodiments relating to blind decoding/search spaceconfiguration and antenna port mapping for EPDCCH transmission will bedescribed.

Blind Decoding/Search Space Configuration for EPDCCH

As described above, EPDCCH transmission may be divided into localizedEPDCCH transmission and distributed EPDCCH transmission. According toone embodiment of the present invention, a UE may configure a searchspace by distinguishing a resource set for localized EPDCCH transmissionfrom a resource set for distributed EPDCCH transmission. Herein, theresource set may be as PRB set or an ECCE, and an eNB may indicate thetransmission type (localized EPDCCH transmission or distributed EPDCCHtransmission) of a resource set through higher layer signaling.

In other words, the UE may perform blind decoding at each aggregationlevel on a resource unit for EPDCCH among a plurality of resource unitsof a subframe (for example, if the resource set is a PRB set, theresource units may be PRB pairs or ECCEs (EREGs) and if the resource setis an ECCE, the ECCE or EREG may be a resource unit). Herein, theresource set may be configured for any one of localized EPDCCHtransmission or distributed EPDCCH transmission.

A more detailed description will be given of examples of FIGS. 7 and 8.In FIGS. 7 and 8, it is assumed that the resource set is a PRB set, andthe resource unit is an ECCE or a PRB pair. While the PRB set isillustrated as having two or four PRB pairs in FIGS. 7 and 8,embodiments of the present invention are not limited thereto. Dependingon configuration, the number of the PRB pairs of a PRB set may be set to2, 4, 8, or the like. In FIGS. 7 and 8, PRB pairs included in adistributed PRB set are illustrated as being consecutive on thefrequency axis for simplicity of illustration. Accordingly, the PRB pairincluded in a distributed PRB set may be considered non-consecutive onthe frequency axis.

FIG. 7(a) illustrates a case in which one PRB set is configured for aUE, and FIG. 7(b) illustrates a case in which two PRB sets areconfigured for the UE. Referring to FIG. 7(a), the UE may recognize,through higher layer signaling, that one PRB set for EPDCCH is provided,and four PRB pairs are for EPDCCH transmission among the other PRB pairsof a subframe. The UE may also recognize whether this PRB set is forlocalized EPDCCH transmission or for distributed EPDCCH transmission.The UE may determine an EPDCCH candidate at each aggregation levelaccording to the transmission type (localized EPDCCH transmission ordistributed EPDCCH transmission) and perform decoding.

In FIG. 7(b), two PRB sets are configured for the UE. It may beindicated through higher layer signaling that one of the two PRB sets isa PRB set for localized EPDDCH (localized PRB set) and the other one isa PRB set for distributed EPDDCH (distributed PRB set). The UE maydetermine an EPDCCH candidate for each PRB set according to eachtransmission type and perform decoding. In the case in which two PRBsets are configured differently from the example of FIG. 7(b), both PRBsets may be for localized (or distributed) EPDCCH.

When two PRB sets (a PRB set for distributed EPDDCH and a PRB set forlocalized EPDDCH) are configured as described above, the PRBs includedin the respective PRB sets may not be mutually exclusive. In otherwords, a PRB pair included in one PRB set may belong to another PRBpair. This case is illustrated in FIG. 8. Referring to FIG. 8, the PRBset for localized EPDDCH transmission includes PRB pair #n to PRB pair#n+3, and the PRB set for distributed EPDDCH transmission includes RBpair #n−1 to PRB pair #n. That is, PRB pair #n is included both in thePRB set for localized EPDDCH transmission and the PRB set fordistributed EPDCCH transmission. If there is an overlapping PRB pairwhich is present in both PRB sets as in the above case, the UE mayconsider only at least one antenna port other than the antenna portsassociated with distributed EPDCCH transmission as being valid on theoverlapping PRB pair, among antenna ports associated with localizedEPDCCH transmission. For example, if antenna ports 107 and 109 areassociated with distributed EPDCCH, and antenna ports 107, 108, 109 and110 are associated with localized EPDCCH, the UE may use only antennaports 108 and 109 to perform blind decoding for the localized EPDCCH inthe overlapping PRB pair. Alternatively, the UE may use only ports 108and 109 to perform blind decoding for the localized EPDCCH. For example,ports may be predefined or indicated through higher layer signaling suchthat a port used for ECCE indexes 0, 1, 2, and 3 of the correspondingPRB pair is fixed to port 108 (or 109), and ECCE indexes 0 and 1 useport 108, and ECCE indexes 2 and 3 use port 109.

As another method for determining the transmission type of a resourceset, a possible pattern may be predefined, and an eNB may signal theindex of the pattern. In this case, it may be assumed that the patternis defined for a certain number of resource units and repeated for allthe resource units. For example, the pattern may be defined by a mappingtable as shown in Table 3 below.

TABLE 3 Resource type index 0 1 2 3 4 5 6 7 8 Transmission type L L L LD D L L L

In Table 3, L denotes localized EPDCCH transmission, and D denotesdistributed EPDCCH transmission. If resource unit indexes of a searchspace which are set through higher layer signaling are 2, 3, 4, 5, 6,and 7, the UE may exclude a resource unit of a specific type from thesearch space based on the signaled indexes. The specific type may bedetermined by higher layer signaling. That is, if a resource unit fordistributed EPDCCH transmission needs to be excluded, resource unitindexes of a search space configured by the UE may be determined to be2, 3, 6, and 7.

Hereinafter, a description will be given of methods to perform antennaport mapping and decoding when an ECCE for localized EPDCCH transmissionand an ECCE for distributed EPDCCH transmission are present together ina one EPDCCH candidate as shown in FIG. 9. Referring to FIG. 9, ECCEsconstituting an EPDCCH candidate of aggregation level 2 include an ECCEfor localized EPDCCH transmission and an ECCE for distributed EPDCCHtransmission. In this case, the UE may perform blind decoding/searchspace configuration using the following methods.

First, the UE may assume that ports for the ECCEs are different fromeach other although the ECCEs are in the same EPDCCH candidate. That is,decoding for the ECCE for distributed EPDCCH transmission may beperformed using a PRB pair (or ECCE) for distributed EPDCCH transmissionand a port defined for distributed EPDCCH transmission and then theresult of decoding may be combined with a result of decoding for theECCE for localized EPDCCH transmission (transmitted through portdifferent from the port for distributed EPDCCH transmission) to performblind decoding. In other words, in FIG. 9, an EPDCCH candidate ofaggregation level 2 for a localized EPDCCH includes an ECCE forlocalized EPDCCH transmission and an ECCE for distributed EPDCCHtransmission, and decoding is performed in the manner that decodingresults for the respective ECCEs are combined together. That is,decoding for one ECCE is performed through a port for the ECCE forlocalized EPDCCH transmission, and decoding for the other ECCE isperformed through another port for the ECCE for distributed EPDCCHtransmission. This may mean that precoding can be performed differentlyfor each ECCE.

Second, blind decoding for the EPDCCH candidate may be skipped. That is,if an ECCE for localized EPDCCH transmission and an ECCE for distributedEPDCCH transmission included in one EPDCCH candidate overlap each other,the UE may recognize such overlap and not perform blind decoding for theEPDCCH candidate.

Third, blind decoding of an EPDCCH candidate may be performed only foran ECCE of a specific transmission type among the ECCEs belonging to theEPDCCH candidate. Herein, the transmission type (localized ordistributed) to be used may be determined based on the priority or thenumber of ECCEs. In the case in which the determination is based on thepriority, an ECCE of a transmission type to be decoded may bepredetermined or indicated through higher layer signaling. In the casein which the determination is based on the number of ECCEs, only theECCEs of the specific transmission type may be used for EPDCCH candidatedecoding if the aggregation level is greater than or equal to 4, or ifthe number of ECCEs of the specific transmission type is greater thanthe number of ECCEs of another transmission type. As another method toperform blind decoding using only ECCEs of the specific transmissiontype, ECCEs of different transmission types may not be included in thesame search space in the process of search space configuration for theUE. That is, a search space only for localized (or distributed) EPDCCHtransmission may be signaled to the UE. Alternatively, if an EPDCCHcandidate of a higher aggregation level is determined based on a loweraggregation level, the EPDCCH candidate of aggregation level 1 may beconfigured only with ECCEs of a specific transmission type.

Hereinafter, a description will be given, with reference to FIG. 10, ofa method of EPDCCH candidate configuration and a decoding method for thecase in which a resource set for localized EPDCCH transmission and aresource set for distributed EPDCCH transmission are present together ina PRB pair. In FIG. 10, it is assumed that one PRB pair has eight EREGsfor simplicity of illustration. However, this example may also beapplied to a case which one PRB pair has 16 EREGs.

In the case in which an EPDCCH candidate of an aggregation level forlocalized EPDCCH transmission includes an EREG for distributed EPDCCHtransmission, the EPDCCH candidate may not be subjected to blinddecoding. For example, if EREG 4 to EREG 7 constitute an EPDCCHcandidate of aggregation level 2, and EREG 6 and EREG 7 are fordistributed EPDCCH transmission in FIG. 10, the EPDCCH candidateincluding EREG 4 to EREG 7 is not subjected to blind decoding.

Alternatively, if an EPDCCH candidate of an aggregation level forlocalized EPDCCH transmission includes an EREG for distributed EPDCCHtransmission, blind decodig for the EPDCCH candidate may be performedusing only EREGs (or ECCEs) configured to be used for a localizedEPDCCH. That is, blind decoding may be performed using only EREG 4 andEREG 5 in FIG. 10. This may be regarded as execution of rate matchingfor EREG 6 and EREG 7. To this end, the start positions of EPDCCHcandidates of different aggregation levels may be set to be differentfrom each other.

Alternatively, if an EPDCCH candidate of an aggregation level forlocalized EPDCCH transmission includes an EREG for distributed EPDCCHtransmission, an offset may be applied to the start position of theEPDCCH candidate such that all the EREGs for a localized EPDCCH arecontained in a PRB pair. That is, in FIG. 10, if PRB pair 0 is forlocalized EPDCCH transmission, PRB pair 1 is for localized anddistributed EPDCCH transmissions, PRB pair 3 is for localized EPDCCHtransmission and EREG 6 and EREG 7 are for distributed EPDCCHtransmission, an EPDCCH candidate positioned at PRB pair 1 may beshifted to PRB pair 2.

Alternatively, if an EPDCCH candidate is for localized EPDCCH, butincludes a resource set (an ECCE or an EREG set) for distributed EPDCCH,the EPDCCH candidate may be configured using the consecutive set indexesexcluding the resource set. That is, in FIG. 10, if all the PRB pairsare localized EPDCCH candidates of aggregation level 4, and EREGs 4, 5,6, and 7 are configured to be used for distributed EPDCCH, resource setsincluded in the EPDCCH candidate may be determined to be EREGs 0, 1, 2,3, 8, 9, 10, and 11.

Antenna Port Configuration/Mapping for EPDCCH

Hereinafter, embodiments will be described in relation tomapping/configuration of antenna ports in an EPDCCH resource set (PRBset, ECCE set, EREG set, etc.).

FIG. 11 illustrates an EPDCCH resource set and antenna port mappingaccording to one embodiment of the present invention. Referring to FIGS.11(a), 11(b), and 11(c), for aggregation levels 1, 2, and 4, the antennaport is allocated by unit of one ECCE, two ECCEs, and four ECCEs. Thatis, the antenna port is mapped according to the aggregation levels. Inother words, an EPDCCH may use one antenna port to ensure schedulingflexibility and reduce decoding time. A mapping relationship between theECCEs and the port may be UE-specifically delivered using apredetermined value (which means that a specific resource determines theport. That is, a resource at a specific position is transmitted througha specific port), or through higher layer signaling.

FIGS. 12 to 13 illustrate port allocation in the case in which localizedEPDCCH transmission and distributed EPDCCH transmission are mixed in onePRB pair according to one embodiment of the present invention.

FIG. 12 illustrates a scheme in which ports other than the port fordistributed EPDCCH transmission are sequentially allocated to ECCEs forlocalized EPDCCH transmission. Referring to FIG. 12, the ports for theECCEs are implicitly or explicitly mapped in the order of indexes 7, 8,9 and 10 in a PRB pair. FIG. 12(a) illustrates an example of implicitallocation, in which a port allocated to a specific ECCE in the PRB pairmay be determined depending on the position of a resource constitutingthe ECCE. As the port is determined depending on the position of theECCE in the implicit allocation, non-consecutive port allocation may bepossible in each PRB pair. That is, as shown in FIG. 12(a), when two orthree ECCEs for distributed EPDCCH transmission are present in a PRBpair, port allocation may be implemented as {7, 9, 10} or {7, 10}. FIG.12(b) illustrates another example of implicit allocation on theassumption that port 10 is for distributed EPDCCH transmission. Tosummarize, in the examples of FIGS. 12(a) and 12(b), port allocation forECCEs for localized EPDCCH transmission may change depending on thepositions of ECCES for distributed EPDCCH transmission and ports.

FIG. 12(c) illustrates explicit allocation. Explicit allocation refersto a scheme in which a UE receives a port to be used for EPDCCH decodingthrough higher layer signaling. Referring to FIG. 12(c), the UE mayrecognize, through higher layer signaling, that ports 7, 8, 9, and 10are mapped to the ECCEs in this order, and allocate the ports other thanthe port for an ECCE for distributed EPDCCH transmission to ECCEs forlocalized EPDCCH transmission in the order signaled.

FIG. 13 illustrates another example of implicit allocation and explicitallocation. Particularly, when implicit allocation is employed, a portused for distributed EPDCCH transmission represents use of a portcorresponding to the position of a corresponding ECCE. If a plurality ofECCEs used for distributed EPDCCH transmission is present in a PRB pair,one of the ports allocated to the ECCE may be used as a port fordistributed EPDCCH transmission.

When it is assumed that the UE implicitly or explicitly determines portmapping of a resource set (ECCE, EPDCCH candidate, and PRB pair) asdescribed above, a mapping that the UE is employing (i.e., atransmission scheme corresponding to the current blind decoding by theUE) may conflict with mapping of the unused transmission type (i.e., thecase in which the UE knows the transmission scheme for the resource, butthis scheme is not the transmission scheme in which the UE is currentlyperforming blind decoding). For example, referring to FIG. 14, if port7, 8, 9, and 10 are implicitly/explicitly allocated to the CCEs in a PRBpair in this order in a transmission mode that the UE is currentlyusing, and the port used for the distributed transmission type that theUE does not use is port 7, the UE cannot use port 7 for the distributedtransmission type. To solve such conflict, the following methods may beused.

First, the ports may be sequentially allocated to the resources that theUE can use, except the antenna port for a transmission type that is notused by the UE. That is, as shown in FIG. 14(a), the UE cannot use tworesource sets in the middle of the ECCEs in a PRB pair, and thus cannotuse port 7. Accordingly, the other ports (ports 8, 9, and 10) may besequentially allocated to the other resource sets. Herein, sequentialallocation means mapping is performed according to the order of indexesof the ECCEs for EPDCCH in a PRB pair.

Second, to reduce interference from a different transmission type, theUE may allocate ports of a code division multiplexing (CDM) group towhich a port used for the different transmission type does not belongfirst, among the ports usable by the UE. This means that ports of theCDM group having the port of the transmission type which is not employedby the UE have lower priority in relation to port reallocation. That is,in FIG. 14, sine the port used for distributed EPDCCH transmission isport 7, ports 9 and 10 belonging to a CDM group different from that ofport 7 may be allocated first. Alternatively, ports of the other CDMgroup may be allocated, and then the remaining ports of the CDM groupincluding the port used for the distributed type may be allocated. Forexample, if the port used for the distributed type is 8, and ECCE indexis #1, antenna ports 7, 9, and 10 or antenna ports 9, 10, and 7 may beallocated to ECCE indexes #0, #2, and #3.

The UE may configure a search space based on the port mapping determinedin the above two methods. At this time, the port/resource related to thetransmission type that the UE does not employ may be excluded from thesearch space. In addition, DMRS configuration for the transmission typethat is not used by the UE may employ a predefined mapping rule or beindicated for the UE through higher layer signaling. Further, bothresources and ports in the descriptions given above are restricted, butit is possible to apply restriction only to the ports. That is, in FIG.14, the UE may reallocate ports to all the resource sets in the PRBpair. In this case, ports may be determined to be used except the portof a transmission type that the UE does not use.

Determination of the Number of Ports for a PRB Pair

Hereinafter, a method for setting the number of antenna ports used ineach PRB pair for EPDCCH will be described. To maximize resourceselectivity in the frequency domain and/or spatial domain, the number ofports for each PRB pair may be determined according to the number of PRBpairs on which EPDCCH transmission is performed and the EPDCCHcandidates of aggregation level 1 (or the number of blind decodings).Further, to enhance the effect of spatial diversity, when two or moreEPDCCH candidates of the same level (e.g., aggregation levels 1 and 2 inlocalized EPDCCH transmission) are present within a PRB pair, blinddecoding may be performed using different ports for the EPDCCHcandidates. In this case, the antenna port numbers used on the PRB pair(i.e., antenna ports used on the PRB pair) may be UE-specificallydetermined by a network according to a transmission scheme such asMU-MIMO and DPS.

For example, the number of ports for each PRB pair used for EPDCCHtransmission by each UE (i.e., the number of EPDCCH candidates for eachPRB pair) may be expressed as N+M in Equation 2 given below.

$\begin{matrix}{N = \left\{ {{\begin{matrix}{\left\lfloor \frac{i}{j} \right\rfloor,} & {i \geq j} \\{1,} & {i < j}\end{matrix}{\sum\limits_{P}^{\;}M}} = \left\{ \begin{matrix}{{i\mspace{14mu}{mod}\mspace{14mu} j},} & {i \geq j} \\{0,} & {i < j}\end{matrix} \right.} \right.} & {{Equation}\mspace{14mu} 2}\end{matrix}$

In Equation 2, N denotes the number of antenna ports that all the PRBpairs configured for EPDCCH transmission for a UE have in common, idenotes the number of EPDCCH candidates (or the number of blinddecodings) for aggregation level 1, j denotes the number of PRB pairsconfigured through higher layer signaling, and P denote a PRB pair setconfigured for EPDCCH transmission. The value of M for each configuredPRB pair may be determined to be 0 or 1, and the sum of values of M forall the configured PRB pairs equals the remainder obtained by dividingthe number of EPDCCH candidates of aggregation level 1 by the number ofconfigured PRB pairs. In Equation 2, if the denominator is greater thanthe numerator, it may be assumed that the UE uses only one antenna portfor all the PRB pairs. In addition, the value of M for the respectivePRB pairs may be determined according to a defined rule (e.g., the valueis set to 1 from the lowest PRB pair index).

FIG. 15 illustrates an example of determining the number of antennaports for each PRB pair according to Equation 2 described above. In FIG.15, the example assumes that the values of M for the PRB pairs aresequentially allocated from the lowest PRB pair index, and that i, thenumber of EPDCCH candidates of aggregation level 1, is 6, and j, thenumber of PRB pairs for EPDCCH configured for the UE, is set to 6, 5, 4,3, and 2.

Additionally, in determining the value of M for each PRB pair, M may beset using a scheme different from the scheme of setting M to 1 from thelowest PRB pair index, such as a scheme of distributing the values of Mwith the values equally spaced in a given PRB pair or a scheme ofsetting the value from a specific PRB pair. In the equally spacingdistribution scheme, when the number of PRB pairs for EPDCCH is 4 inFIG. 15, the number of ports may be determined to be 2, 1, 2, and 1 forthe respective PRB pairs (in this case, N is set to 1, 1, 1, and 1, andM is set to 1, 0, 1, and 0 for the respective PRB pairs).

Search Space Configuration in Consideration of Channel Estimation

A PDSCH is not transmitted on a PRB pair on which an EPDCCH istransmitted, and the number of the resources available on the PRB pairis greater than that of the resources necessary for EPDCCH transmission.Accordingly, multiple EPDCCHs are preferably transmitted on one PRBpair. In this case, the search space allocation by the UE maysignificantly affect the EPDCCH demodulation performance. For example,as shown in FIG. 16, when the position of each EPDCCH candidate isdetermined, EPDCCH decoding performance may significantly changedepending on channel conditions. More specifically, in FIG. 16, EPDCCHcandidates for each aggregation level are consecutively positioned onthe frequency axis. In this case, if a specific frequency band in whichEPDCCH candidates for a UE are concentrated is subjected to, forexample, deep fading, the EPDCCH demodulation performance of the UE maybe greatly degraded.

Another situation to be considered for allocation of an EPDCCH searchspace is a case in which two EPDCCHs are transmitted to the UE within asubframe. That is, an EPDCCH for DL grant and an EPDCCH for UL grant maybe transmitted respectively. Preferably, such EPDCCHs are transmitted onthe same PRB pair for beamforming gain.

Accordingly, in one embodiment of the present invention, a search spaceis configured according to the following rules, considering the abovediscussion.

First, PRB pairs constituting a search space for a UE are split andallocated in the frequency domain.

Second, the position of EPDCCH candidates corresponding to aggregationlevel 1 is restricted to two ECCEs per PRB pair. The ECCEs to be used asthe position of the EPDCCH candidates for the UE may be indicated forthe UE through RRC signaling. In addition, to lower signaling overhead,the search space is signaled PRB pair by PRB pair in indicating thesearch space through RRC signaling, and the position of the EPDCCHcandidates on each PRB pair may be configured according to a predefinedrule.

An example of search space configuration according to the rulesdescribed above is illustrated in FIG. 17. In FIG. 17, it is assumedthat ECCE to port mapping for each PRB pair uses a combination of {7, 8,9, 10} and that the number of blind decodings for aggregation levels 1,2 and 4 are 8, 8, and 2, respectively. This assumption is for simplicityof illustration, and there may be various examples complying with theabove rules regardless of aggregation levels and the number of blinddecodings. In addition, in FIG. 17, the number for the position ofEPDCCH candidates for each aggregation level corresponds to an antennaport for demodulation of the EPDCCH.

Referring to FIG. 17, EPDCCH channel estimation for each PRB pair iscompleted when it is performed once or twice at all aggregation levels.Accordingly, when the rules described above are followed, configurationof the search space may be implemented with the minimized number ofchannel estimations.

The example of FIG. 17 may also be embodied in the following manner. Theport for each EPDCCH candidate may be configured through a combinationof signaling of resource (e.g., ECCE)-to-port mapping and signaling ofthe search space definition. In signaling the resource-to-port mapping,a pattern of the same port mapping (for example, mapping, when fourECCEs are present in each PRB pair and indexed as 0, 1, 2, and 3 in eachPRB pair, ECCE0 to port 7, ECCE1 to port 8, ECCE2 to port 9, and ECCE3to port 10) may be signaled on all PRB pairs (e.g., PRB pairs on whichEPDCCH is transmitted), or a different pattern of port mapping may besignaled for each PRB pair. Herein, the search space definition refersto a process of indicating, by an eNB, EPDCCH candidates for which theUE needs to perform blind decoding. The EPDCCH candidates for eachaggregation level may be indicated for the UE by applying theaforementioned rule which prescribes that EPDCCH candidates ofaggregation level 1 are restricted to two ECCEs per PRB pair configuredfor EPDCCH transmission. In this process, ports for the respectiveEPDCCH candidates may be defined in conjunction with the independentlysignaled port mapping. For an EPDCCH candidate of an aggregation levelhigher than or equal to 2, one of the ports for aggregation level 1EPDCCH candidates (or ECCEs if aggregation level 1 EPDCCH candidates arenot included) constituting the EPDCCH candidate may be selected.

Relationship Between EPDCCH and Demodulation RS Port

Hereinafter, a description will be given of a method of determining aDMRS port that the UE uses in detecting an EPDCCH (i.e., ECCE to portmapping). Specifically, a description will be given of a method ofmapping between a resource set (e.g., an ECCE) on which EPDCCH istransmitted and a DMRS port for EPDCCH demodulation and a method forsignaling the mapping. In the following description, it is assumed thateach PRB pair has four ECCEs as shown in FIG. 18.

The first method is to configure a port combination table and signal theindexes of the port combinations such that a port combinationcorresponding to an index is used for each of the PRB pairs. That is,all combinations of four RS ports may be listed to map an antenna portto each ECCE, and the network may indicate indexes of UE-specific orcell-specific RS port combinations through higher layer signaling. Inthis case, an MU-MIMO-based EPDCCH may be implemented, and inter-cell RScollision may be avoided. An example of the indexes of the combinationsis shown in FIG. 4.

TABLE 4 Index {ECCE0, ECCE1, ECCE2, ECCE3} 0 {7, 8, 9, 10} 1 {7, 8, 10,9} 2 {7, 9, 8, 10} 3 {7, 9, 10, 8} . . . . . . 23  {10, 9, 8, 7}

The second method, which is based on the first method, is to signal anindex for each PRB pair. 5 bits are needed to implement such signaling,but some of the combinations may be eliminated to lower signalingoverhead. For example, in configuring a combination, antenna ports forconsecutive ECCEs may belong to different CDM groups. That is, onlycombinations such as {7, 9, 8, 10} and {9, 7, 10, 8} may be considered.In the case in which these combinations are used, RS collision betweenECCEs using the same time/frequency resources may be avoided whenneighboring cells use the same time/frequency resources for EPDCCHtransmission.

The combinations described above are configured such that ECCEsconstituting a PRB pair use different ports, but the table may include acase in which consecutive ECCEs use the same port. That is, patternssuch as {7, 7, 9, 9}, {8, 8, 10, 10}, {7, 7, 8, 8}, {9, 9, 10, 10}, {7,7, 7, 7}, and {8, 8, 8, 8} may be added to Table 4. These patterns maybe implemented in the form of {a, a, b, b}, {a, b, b, b}, {a, a, a, b},{a, b, b, a}, and {a, a, a, a}. In the case in which identical ports arepresent in a PRB pair, the combinations may be useful when the ECCEshaving the same port are used at different transmission points. Tosupport such operations, virtual cell IDs may be grouped, and one of thepatterns may be used in each group.

The third method is to link results of modulo operation for the virtualcell IDs to the aforementioned indexes. In other words, this method isto tie the indexes to another parameter signaled for an EPDCCH RS.

More specifically, a scrambling sequence for a DMRS may be derived fromEquation 3 given below.c _(init)=(└n _(s)/2┘+1)·(2X+1)·2¹⁶ +n _(SCID)  Equation 3

In Equation 3, X and n_(SCID) may be contained and signaled in the DCIformat. Equation 3 may be used even for an EPDCCH DMRS. However, in thecase of EPDCCH, use of the DCI format is not allowed, and thus n_(SCID)may be fixed to a specific value, and parameter X may be indicatedthrough RRC signaling. Accordingly, modulo operation may be performedfor parameter X signaled for the DMRS scrambling sequence to derive anindex in an ECCE-to-port mapping table. Specifically, for example, ifthe ECCE-to-port mapping table is given as Table 4, the UE may determinethe DMRS scrambling sequence index through modulo operation (X modulo24).

FIG. 19 is a diagram illustrating configurations of a transmission pointapparatus and a UE according to one embodiment of the present invention.

Referring to FIG. 19, a transmission point apparatus 1910 may include areceive module 1911, a transmit module 1912, a processor 1913, a memory1914, and a plurality of antennas 1915. The antennas 1915 represent atransmission point apparatus that supports MIMO transmission andreception. The receive module 1911 may receive various signals, data andinformation from a UE on uplink. The transmit module 1912 may transmitvarious signals, data and information to a UE on downlink. The processor1913 may control overall operation of the transmission point apparatus1910.

The processor 1913 of the transmission point apparatus 1910 according toone embodiment of the present invention may perform operations necessaryfor the embodiments described above.

Additionally, the processor 1913 of the transmission point apparatus1910 may function to operationally process information received by thetransmission point apparatus 1910 or information to be transmitted tothe outside, etc. The memory 1914, which may be replaced with an elementsuch as a buffer (not shown), may store the processed information for apredetermined time.

Referring to FIG. 19, a UE 1920 may include a receive module 1921, atransmit module 1922, a processor 1923, a memory 1924, and a pluralityof antennas 1925. The antennas 1925 mean that the UE supports MIMOtransmission and reception. The receive module 1921 may receive varioussignals, data and information from an eNB on downlink. The transmitmodule 1922 may transmit various signals, data and information to theeNB on uplink. The processor 1923 may control overall operation of theUE 1920.

The processor 1923 of the UE 1920 according to one embodiment of thepresent invention may perform operations necessary for the embodimentsdescribed above.

Additionally, the processor 1923 may function to operationally processinformation received by the UE 1920 or information to be transmitted tothe outside, and the memory 1924, which may be replaced with an elementsuch as a buffer (not shown), may store the processed information for apredetermined time.

The configurations of the transmission point apparatus and the UE asdescribed above may be implemented such that the above-describedembodiments are independently applied or two or more thereof aresimultaneously applied, and description of redundant parts is omittedfor clarity.

Description of the transmission point apparatus 1910 in FIG. 19 may alsobe applied to a relay which serves as a downlink transmitter or anuplink receiver, and description of the UE 1920 may be applied to arelay which serves as a downlink receiver or an uplink transmitter.

The embodiments of the present invention may be implemented throughvarious means, for example, hardware, firmware, software, or acombination thereof.

When implemented by hardware, a method according to embodiments of thepresent invention may be embodied as one or more application specificintegrated circuits (ASICs), one or more digital signal processors(DSPs), one or more digital signal processing devices (DSPDs), one ormore programmable logic devices (PLDs), one or more field programmablegate arrays (FPGAs), a processor, a controller, a microcontroller, amicroprocessor, etc.

When implemented by firmware or software, a method according toembodiments of the present invention may be embodied as a module, aprocedure, or a function that performs the functions or operationsdescribed above. Software code may be stored in a memory unit andexecuted by a processor. The memory unit is located at the interior orexterior of the processor and may transmit and receive data to and fromthe processor via various known means.

Preferred embodiments of the present invention have been described indetail above to allow those skilled in the art to implement and practicethe present invention. Although the preferred embodiments of the presentinvention have been described above, those skilled in the art willappreciate that various modifications and variations can be made in thepresent invention without departing from the spirit or scope of theinvention. For example, those skilled in the art may use a combinationof elements set forth in the above-described embodiments. Thus, thepresent invention is not intended to be limited to the embodimentsdescribed herein, but is intended to have the widest scope correspondingto the principles and novel features disclosed herein.

The present invention may be carried out in other specific ways thanthose set forth herein without departing from the spirit and essentialcharacteristics of the present invention. Therefore, the aboveembodiments should be construed in all aspects as illustrative and notrestrictive. The scope of the invention should be determined by theappended claims and their legal equivalents, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. The present invention is not intendedto be limited to the embodiments described herein, but is intended tohave the widest scope consistent with the principles and novel featuresdisclosed herein. In addition, claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention as described above areapplicable to various mobile communication systems.

The invention claimed is:
 1. A method for receiving control informationby a user equipment (UE) in a wireless communication system, the methodcomprising: receiving, via higher layer signaling, an enhanced physicaldownlink control channel (EPDCCH) configuration including a scramblingsequence parameter for an EPDCCH demodulation reference signal (DMRS);obtaining an EPDCCH DMRS sequence based on an equation ‘(└n_(s)/2┘+1)·(2X+1)·2¹⁶+n_(SCID)’, where ‘n_(s)’ denotes a slot number, ‘X’denotes the EPDCCH DMRS scrambling sequence parameter included in theEPDCCH configuration and ‘n_(SCID)’ denotes a scrambling identity forthe EPDCCH DMRS; and obtaining downlink control information (DCI)through an EPDCCH using the EPDCCH DMRS sequence, wherein the scramblingidentity ‘n_(SCID)’ for the EPDCCH DMRS is fixed to a predeterminedvalue.
 2. The method of claim 1, wherein the scrambling identity‘n_(SCID)’ does not depend on scrambling identity information in theDCI.
 3. The method of claim 1, wherein obtaining the DCI through theEPDCCH comprises: performing demodulation for the EPDCCH using theEPDCCH DMRS sequence.
 4. The method of claim 1, wherein obtaining theDCI through the EPDCCH comprises: performing blind decoding on aplurality of physical resource block (PRB) pairs corresponding to eachof at least one EPDCCH PRB set based on the EPDCCH configuration.
 5. Themethod of claim 4, wherein the PRB pairs for the EPDCCH is determinedbased on information on a resource set in the EPDCCH configuration. 6.The method of claim 4, wherein each of the PRB pairs comprises fourenhanced control channel elements (ECCEs), and each of the ECCEscomprises four enhanced resource element groups (EREGs).
 7. The methodof claim 1, wherein the EPDCCH configuration indicates whether theEPDCCH corresponds to localized EPDCCH transmission or distributedEPDCCH transmission.
 8. A non-transitory computer readable mediumrecorded thereon a program for executing the method of claim
 1. 9. Auser equipment (UE) comprising: a receiver to receive, via higher layersignaling, an enhanced physical downlink control channel (EPDCCH)configuration including a scrambling sequence parameter for an EPDCCHdemodulation reference signal (DMRS), and to receive downlink controlinformation (DCI) through an EPDCCH using a EPDCCH DMRS sequence; and aprocessor to obtain the EPDCCH DMRS sequence based on an equation‘(└n_(s)/ 2┘+1)·(2X+1)·2¹⁶+n_(SCID)’, where ‘n_(s)’ denotes a slotnumber, ‘X’ denotes the EPDCCH DMRS scrambling sequence parameterincluded in the EPDCCH configuration and ‘n_(SCID)’ denotes a scramblingidentity for the EPDCCH DMRS, wherein the scrambling identity ‘n_(SCID)’for the EPDCCH DMRS is fixed to a predetermined value.
 10. The UE ofclaim 9, wherein the scrambling identity ‘n_(SCID)’ does not depend onscrambling identity information in the DCI.
 11. The UE of claim 9,wherein the processor performs demodulation for the EPDCCH using theEPDCCH DMRS sequence.
 12. The UE of claim 9, wherein the processorperforms blind decoding on a plurality of physical resource block (PRB)pairs corresponding to each of at least one EPDCCH PRB set based on theEPDCCH configuration.
 13. The UE of claim 12, wherein the PRB pairs forthe EPDCCH is determined based on information on a resource set in theEPDCCH configuration.
 14. The UE of claim 12, wherein each of the PRBpairs comprises four enhanced control channel elements (ECCEs), and eachof the ECCEs comprises four enhanced resource element groups (EREGs).15. The UE of claim 9, wherein the EPDCCH configuration indicateswhether the EPDCCH corresponds to localized EPDCCH transmission ordistributed EPDCCH transmission.